U.S. patent number 7,080,507 [Application Number 10/758,268] was granted by the patent office on 2006-07-25 for exhaust gas purifier.
This patent grant is currently assigned to Hitachi Car Engineering Co., Ltd., Hitachi, Ltd.. Invention is credited to Kozo Katogi, Masami Nagano, Shinji Nakagawa, Hiroshi Sekine, Hiroyuki Takamura.
United States Patent |
7,080,507 |
Katogi , et al. |
July 25, 2006 |
Exhaust gas purifier
Abstract
In order to improve the decrease of the catalytic action and the
deterioration of the exhaust purification performance, a catalyst
installed in the exhaust pipe of an engine and a secondary air pump
for supplying secondary air into the exhaust pipe are provided, and
the secondary air pump is operated even after the engine has
stopped.
Inventors: |
Katogi; Kozo (Hitachi,
JP), Nagano; Masami (Hitachinaka, JP),
Sekine; Hiroshi (Hitachinaka, JP), Takamura;
Hiroyuki (Hitachinaka, JP), Nakagawa; Shinji
(Hitachinaka, JP) |
Assignee: |
Hitachi, Ltd. (Tokyo,
JP)
Hitachi Car Engineering Co., Ltd. (Hitachinaka,
JP)
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Family
ID: |
32652794 |
Appl.
No.: |
10/758,268 |
Filed: |
January 16, 2004 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20040200212 A1 |
Oct 14, 2004 |
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Foreign Application Priority Data
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Jan 20, 2003 [JP] |
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2003-010502 |
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Current U.S.
Class: |
60/289; 60/299;
60/285 |
Current CPC
Class: |
F01N
13/009 (20140601); F01N 3/22 (20130101); F01N
11/002 (20130101); F01N 3/32 (20130101); F01N
2230/04 (20130101); F01N 2430/06 (20130101); Y02T
10/40 (20130101); F02B 37/00 (20130101); F01P
2031/30 (20130101); Y02T 10/12 (20130101); Y02T
10/47 (20130101); Y02T 10/20 (20130101) |
Current International
Class: |
F01N
3/00 (20060101) |
Field of
Search: |
;60/285,289,299,290 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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196 08 060 |
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Jul 1997 |
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DE |
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05-079319 |
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Mar 1993 |
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JP |
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2000-352338 |
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Dec 2000 |
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JP |
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2001-241319 |
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Sep 2001 |
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JP |
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2003-027987 |
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Jan 2003 |
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JP |
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Other References
Shinji Nakagawa, et al., "A New Air-Fuel Ratio Feed Back Control
for ULEV/SULEV Standard," SAE Technical Paper Series, 2002-01-0194.
cited by other.
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Primary Examiner: Denion; Thomas
Assistant Examiner: Tran; Diem
Attorney, Agent or Firm: Crowell & Moring LLP
Claims
What is claimed is:
1. An exhaust gas purifier comprising a catalyst installed in the
exhaust pipe of an engine and a secondary air pump for supplying
secondary air into the exhaust pipe, wherein said secondary air
pump is operated for a specific length of time after the engine has
stopped when any of the water temperature sensor, suction air
temperature sensor, catalyst temperature sensor and exhaust pipe
temperature sensor of the engine is judged to have failed.
2. An exhaust gas purifier according to claim 1, further comprising
at least one of a means for measuring and a means for estimating
the exhaust pipe temperature of the engine, wherein said secondary
air pump is operated for a specified length of time after the
engine has stopped when the measured or estimated exhaust pipe
temperature is outside a specified range.
3. An exhaust gas purifier according to claim 1, wherein a
secondary air inlet is provided near the exhaust valve of the
engine.
4. An exhaust gas purifier according to claim 1, wherein a
secondary air inlet is provide in the upstream side of the
catalyst.
5. An exhaust gas purifier according to claim 1, wherein a
secondary air inlet is provide in the downstream side of the
catalyst.
6. An exhaust gas purifier according to claim 1, wherein said
secondary air pump operates intermittently.
7. An exhaust gas purifier according to claim 1, wherein the number
of revolutions of said secondary air pump after the engine has
stopped is less than that while the engine is in operation.
8. An exhaust gas purifier according to claim 1, further comprising
a fuel pressure regulating means for regulating the fuel pressure
in a fuel pipe, wherein the fuel pressure in said fuel pipe is
reduced after the engine has stopped.
9. An exhaust gas purifier according to claim 8, wherein said fuel
pressure regulating means is a bypass valve installed in parallel
with a fuel pressure regulating valve.
10. An exhaust gas purifier according to claim 8, wherein said fuel
pressure regulating means is a fuel pump for supplying fuel from a
fuel tank to an injector and the fuel pressure in the fuel pipe is
reduced by rotating the fuel pump in reverse.
11. An exhaust gas purifier according to claim 1, further
comprising at least one of a means for measuring and a means for
estimating the catalyst temperature, wherein said secondary air
pump is operated in accordance with the measured or estimated
catalyst temperature.
12. An exhaust gas purifier according to claim 11, further
comprising at least one a means for measuring and a means for
estimating ambient temperature, wherein said secondary air pump is
operated in accordance with the measured or estimated ambient
temperature and measured or estimated catalyst temperature.
13. An exhaust gas purifier according to claim 11, wherein said
secondary air pump is operated for a specified length of time after
the engine has stopped when the measured or estimated catalyst
temperature is outside a specified range.
14. An exhaust gas purifier comprising a catalyst installed in the
exhaust pipe of an engine and a secondary air pump for supplying
secondary air into the exhaust pipe, wherein said secondary air
pump is operated after the engine has stopped and further
comprising a controller for controlling the suction valve, exhaust
valve, throttle valve and ISC valve of the engine, wherein said
suction valve, exhaust valve, throttle valve and ISC valve are
fully opened after the engine has stopped.
15. An exhaust gas purifier according to claim 14, wherein said
secondary air pump is operated for a specified length of time after
the engine has stopped.
16. An exhaust gas purifier comprising a catalyst installed in the
exhaust pipe of an engine and a secondary air pump for supplying
secondary air into the exhaust pipe, wherein said secondary air
pump is operated after the engine has stopped and further
comprising a means for rotating the crank shaft of the engine,
wherein said crank shaft is rotated for a specified number of times
or up to a specified crank angle after the engine has stopped.
Description
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust gas purifier of an
engine and a controller thereof.
According to a prior art, in order to remove toxic contents in the
exhaust gas of an engine, for example, unburnt hydro carbon
compound (HC), carbon monoxide (CO) and nitrogen oxides (NOx),
there has been disclosed an exhaust gas purifier that is equipped
with a catalytic converter rhodium installed in an exhaust pipe and
converts them to non-toxic components by catalytic action.
With this purifier, however, since the catalytic action depends
upon the catalyst temperature, the catalytic action cannot be
performed until the catalyst temperature increases after the engine
has started. Thus, there has been disclosed another exhaust gas
purifier that have the toxic contents in the exhaust gas absorbed
into the catalyst up to a certain volume temporarily and then
purifies them under a temperature higher than the specified
(Japanese Patent Application Laid-open No. Hei 05-79319
(1993)).
With the prior art as above, however, exhaust gas remains in the
exhaust pipe and exhaust gas purifier after the engine has stopped.
Because of this, there has been a problem that water content in the
residual exhaust gas liquefies and adheres onto the surface of the
catalyst, causing another problem that the catalyst temperature
increase is delayed due to the decrease of the contact area between
the catalyst and exhaust gas and vaporization of the adhered water
content at the next engine start and so the purification
performance lowers. Besides, if a sudden change in the catalyst
temperature is caused, temperature difference is generated between
the portions with and without adhered water and the catalyst may
possibly break due to thermal stress.
SUMMARY OF THE INVENTION
The present invention is made in view of the above problems and its
object is to improve the purification performance and reliability
of the exhaust gas purifier.
In order to solve the problems, the present invention is equipped
with a catalyst installed in the exhaust pipe of an engine and a
secondary air pump for supplying secondary air into the exhaust
pipe, and operates the secondary air pump in accordance with the
operating condition of the engine.
Besides, the present invention is equipped with a catalyst
installed in the exhaust pipe of an engine and a secondary air pump
for supplying secondary air into the exhaust pipe, and operates the
secondary air pump after the engine has stopped.
BRIEF DESCRIPTION OF DRAWINGS
The present invention will be understood more fully from the
detailed description given hereinafter and from the accompanying
drawings of the preferred embodiment of the present invention,
which, however, should not be taken to be limitative to the
invention, but are for explanation and understanding only.
In the drawings:
FIG. 1 is a diagram showing the engine construction of an
embodiment of the present invention.
FIG. 2 is an explanatory drawing of the engine controller.
FIG. 3 is a control block diagram of the present invention.
FIG. 4 is an explanatory drawing on the temperature estimation.
FIG. 5 is an explanatory drawing on the catalyst temperature
control.
FIG. 6 is an explanatory timing chart of the control.
FIG. 7 is an explanatory flow chart of the control.
FIG. 8 is an explanatory drawing on the timer control during
idling.
FIG. 9 is an explanatory drawing on the operating time setting for
the secondary air pump.
FIG. 10 is an explanatory drawing on the connection switching
circuit for the secondary air pump.
FIG. 11 is an explanatory drawing on the diagnosis and fail-safe
function.
FIG. 12 is an explanatory drawing on a countermeasure against
unburnt HC in the combustion chamber.
FIG. 13 is an explanatory drawing on letting the secondary air near
the exhaust valve.
FIG. 14 is a view showing a separate secondary air pump
controller.
FIG. 15 is an explanatory drawing on letting the secondary air into
the downstream side of the catalyst.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention will be discussed hereinafter in detail in
terms of the preferred embodiment of an exhaust gas purifier
according to the present invention with reference to the
accompanying drawings. In the following description, numerous
specific details are set forth in order to provide a thorough
understanding of the present invention. It will be obvious,
however, to those skilled in the art that the present invention may
be practiced without these specific details. In other instance,
well-known structures are not shown in detail in order to avoid
unnecessary obscurity of the present invention.
Preferred embodiments of the exhaust gas purifier according to the
present invention are described hereunder, using figures.
FIG. 1 shows the construction of the engine relating to the present
invention. An engine 100 comprises an injector 101, ignition plug
102, ignition coil 103, throttle 104, water temperature sensor 110,
crank angle sensor 111, cam angle sensor 112, throttle position
sensor 113, suction pipe pressure sensor 114 or suction air
flowmeter 115, secondary air pump 124, and catalyst 118 equipped
with a catalyst temperature sensor 123, which all are connected to
an engine controller 120.
Fuel is supplied from a fuel tank 125 by a fuel pump 117, and the
fuel pressure is kept constant by a fuel pressure regulating valve
119. Besides, there is provided a fuel bypass valve 126 for
bypassing the fuel pressure regulating valve to fail-safe the fuel
pressure.
To measure the suction air temperature and exhaust temperature to
be used as control parameter of the engine, there are installed a
suction air temperature sensor 121 and exhaust temperature sensor
122.
Besides, there is provided a bridge circuit capable of reversing
the voltage to be applied to the fuel pump or a gear device capable
of switching the rotational direction (normal and reverse) of the
fuel pump. With this, the fuel pressure can be decreased, as
required, by rotating the fuel pump in reverse.
FIG. 2 shows a brief composition of the engine controller.
The engine controller comprises a CPU 401 that runs numeric and
logical operation, ROM 402 that at least stores the programs
executed by the CPU 401 and data thereof, RAM 403 that stores data
temporarily, AID converter 404 that receives analog voltage signals
from the sensors, digital input circuit 405 that receives switch
signals showing the operating conditions, pulse input circuit 406
that counts the time interval of pulse signals or number of pulses
in a specified length of time, and also a digital output circuit
407 that switches on and off an actuator (not shown) based on the
computation result of the CPU, pulse output circuit 408 that
outputs a timer count, and communication circuit 409. With the
communication circuit 409, data in the engine controller can be
sent to the outside and the internal condition of the engine
controller can be changed from the outside using communication
commands.
The engine controller that receives an output from the suction pipe
pressure sensor or suction air flowmeter, converts the sensor
voltage, using a table, and calculates the actual suction air
volume Qa per unit time.
The engine controller also measures the pulse signal of the crank
angle sensor and calculates the engine rotational speed NDATA based
on the number of pulses in a specified length of time or time
interval of the pulses.
Dividing the suction air volume Qa per unit time by NDATA and then
by the number of cylinders, the suction air volume Qacyl per cycle
of each cylinder is calculated.
Multiplying Qacyl by the specific coefficient KTI and then by a
correction coefficient including an air-fuel ratio control
correction variable, to be explained later, the fuel volume TI that
can be burnt with Qacyl is obtained and, by opening the injector
for a specified length of time, necessary volume of fuel is
injected to generate air-fuel mixture in every combustion.
The correction coefficient COEF.sub.n as follows is multiplied in
computing TI. TI=COEF.sub.n.times.KTI.times.Qacyl
COEF.sub.n includes an air-fuel ratio correction coefficient
ALPHA.sub.n. COEF.sub.n=1+ALPHA.sub.n+increase correction
factor
If the control is made on each cylinder, individual parameter is
specified, varying the subscript n from 1 to each cylinder
number.
The exhaust gas from the combustion in the combustion chamber
contains toxic substances such as NOx and unburnt HC. Since these
substances result in air pollution if discharged into the air as
they are, NOx and HC are decomposed and purified into N.sub.2,
H.sub.2O and CO.sub.2 inside the catalyst before discharge. In
order to decompose and purify the toxic substances efficiently
inside the catalyst, it is essential to operate the engine at an
air-fuel ratio that realizes high purification efficiency of the
catalyst.
Generally speaking, if an engine is operated under a stoichiometric
condition (theoretical air-fuel ratio), toxic substances in the
exhaust gas is decom posed and purified inside the catalyst.
For example, a chemical reaction mentioned below is caused under a
stoichiometric condition.
C.sub.mH.sub.n+(m+n/2)O.sub.2.fwdarw.mCO.sub.2+n/2H.sub.2O
Since hydro carbon contained in gasoline has higher carbon content
m, an approximation of n=2.times.m is applied and the following
approximation expression can be obtained.
C.sub.mH.sub.2m+(2m)O.sub.2.fwdarw.mCO.sub.2+mH.sub.2O
Each is converted to "mole" unit as follows.
C.sub.mH.sub.2m=m.times.14 g 2mO.sub.2=m.times.64 g
Although hydro carbon is not defined in the above approximation,
the calculation means that 64 g of hydrogen is generally needed for
14 g of gasoline and 18 g of water is generated if specific
gasoline composition is defined. It is generally said that the air
in the volume of about 14.7 times the weight of gasoline is needed
in ideal combustion and water of about 1.4 times the weight of
gasoline is generated.
The water resulting from the combustion of the fuel is in vapor
phase if the exhaust gas temperature is above the due-point
temperature (100.degree. C. under normal condition) but adheres
onto the exhaust pipe inside if the exhaust pipe temperature is
below the due-point temperature. For the same reason, the water
adheres on or is absorbed by the catalyst if the catalyst
temperature is cooled below the due-point temperature.
Catalyst has a characteristic that higher exhaust gas purification
action is performed if the contact area between the exhaust gas and
catalyst metal is wider, and therefore, if the catalyst temperature
is low, there arises a problem that the contact area between the
exhaust gas and catalyst metal is decreased due to the water
content adhered on or absorbed by the catalyst and that the
purification performance of the catalyst lowers. Besides, if a
sudden change in the catalyst temperature is caused, temperature
difference is generated between the portions with and without
adhered water and the catalyst may possibly break due to thermal
stress.
To prevent the above, the present invention realizes the combustion
control in accordance with the exhaust gas temperature.
For example, as shown in FIG. 3, using a means for measuring or
estimating the catalyst temperature and a means for measuring or
estimating the exhaust pipe temperature, there is provided a water
content estimating means that estimates the water content remaining
in the exhaust pipe based on the temperature information.
Thereby, the secondary air pump is operated in accordance with the
engine operating condition.
In other words, during the engine operation, if the catalyst
temperature is above a specified temperature, the secondary air
pump is operated so that the exhaust gas is purified in the
catalyst.
In the case after the engine has stopped, the secondary air pump is
operated to cool down the exhaust pipe until the catalyst
temperature becomes below the specified, that is, below the
due-point temperature.
In addition, by providing an HC emission preventing means inside
the exhaust pipe and controlling the fuel pipe pressure as well as
suction valve, exhaust valve, throttle valve, ISC valve, etc.
accordingly, emission of unburnt HC can be prevented.
If the exhaust temperature can be measured, the combustion control
is performed directly in accordance with the exhaust temperature.
That is, voltage of the exhaust temperature sensor 122 is inputted
and converted to the exhaust pipe temperature.
In the case of estimating the exhaust temperature, to begin with,
voltage of the suction air temperature sensor or water temperature
sensor is inputted and converted to suction temperature or water
temperature, which in turn is set as the initial value of the
exhaust pipe temperature of catalyst temperature. Then, using the
total SGMTI of the fuel volume TI that can be burnt with Qacyl, the
suction air volume per cycle of each cylinder, or the total SGMQA
of the suction air volume QA, and the suction air temperature, the
exhaust pipe temperature is estimated as shown in FIG. 4. Instead,
the catalyst temperature can be estimated in a similar manner.
However, because the catalyst temperature further increases when it
reaches a certain temperature, approximately 300.degree. C., as HC
reacts due to the catalytic action, air-fuel ratio is also used as
one of the variables for estimating the catalyst temperature.
Until the exhaust pipe temperature reaches a specified temperature
after the engine has started, the air-fuel ratio correction
variable of each cylinder is set to a value other than zero so as
to supply unburnt HC and oxygen into the exhaust pipe at the same
time to let them react inside the exhaust pipe. The exhaust pipe
temperature can be increased quickly by reaction heat.
After the exhaust pipe temperature has reached the specified
temperature, the air-fuel correction efficient is set to zero so as
to stop the temperature increase control. As shown in FIG. 5, when
the exhaust pipe temperature or catalyst temperature is above the
temperature increase control start temperature, the air-fuel ratio
correction efficiency is varied for each cylinder. Then, when the
exhaust pipe temperature or catalyst temperature has reached a
specified temperature, the correction variable is set to zero.
The temperature increase control of the exhaust pipe does not
necessarily employ the temperature as a threshold but any of the
time elapsed after engine stop, water temperature, total suction
air volume, total fuel injection volume can be used as the
threshold.
Another means for increasing the exhaust pipe temperature is to so
adjust the ignition timing that the combustion gas at relatively
high temperature is discharged into the exhaust pipe. Besides, in
setting the above-mentioned air-fuel ratio correction coefficient
for each cylinder, correction range is limited because, if the
volume of unburnt HC increases more than what can be processed in
the catalyst, the exhaust gas level lowers. In order to increase
the exhaust pipe temperature without increasing the correction
range, it is also possible to let the ambient air into the exhaust
pipe and accelerate the reaction inside the exhaust pip.
As a means for letting the air into the exhaust pipe, a secondary
air inlet means for the exhaust pipe is used and the ambient air is
supplied by an air pump. It is also permissible that a check valve
is employed so that the ambient air is sucked when the exhaust pipe
pressure becomes lower than that of the ambient air.
With a turbo type engine system, it is permissible that the air
compressed by the turbo is supplied into the exhaust pipe through a
regulating valve.
If the water content remaining in the exhaust gas after the engine
has stopped adheres or condenses on the catalyst, the catalytic
performance lowers at the next engine start as explained
previously. To remove the water content in the exhaust gas
remaining in the exhaust pipe after the engine has stopped, the
secondary air pump is operated to replace the gas in the exhaust
pipe with the ambient air.
In this replacement, a length of time of operating the air pump
after the engine stop shall be equal to or longer than the time to
fill the exhaust pipe volume corresponding to the pump discharge.
Otherwise, the pump shall be operated until the exhaust pipe
temperature becomes lower than a specified time.
FIG. 6 is a timing chart.
Catalyst temperature increase control is performed after a
specified operating condition is met after the engine start and
until a specified time has elapses and, at the same time, the
exhaust pipe temperature TEX is lower than the specified.
A specified operating condition can be a condition where, for
example, the water temperature is higher than 20.degree. C. and, at
the same time, the rotational speed of the engine is lower than the
idling speed by several thousands r/min.
As a means of the catalyst temperature increase control, an
air-fuel ratio correction efficiency is specified for each cylinder
in the case of individual air-fuel ratio control of cylinders.
Using the time elapsed as an argument, a correction coefficient for
each cylinder is searched from a data table and necessary
interpolation is given. Otherwise, using data tables provided for
each rich side and lean side, three different levels of
coefficient, rich-side, lean-side, and no-correction
(stoichiometric), are selected one by one for every injection
timing and the fuel is injected accordingly so that no cylinder is
set under a fixed rich, lean or stoichiometric condition.
If exhaust pipe temperature sensor is not available, it is possible
to estimate the exhaust temperature according to the total suction
air volume or total fuel injection volume, using the suction air
temperature as an initial value, and a value filtered at every unit
time is regarded as the exhaust pipe temperature.
During the individual air-fuel ratio control of cylinders, the air
pump is operated to let the secondary air into the suction pipe.
When a turbo charger is available, the compressed output of the
turbo is sent into the exhaust pipe.
Exhaust gas in the exhaust pipe is purged out according to the
exhaust pipe temperature TEX and ambient air temperature TAMB after
the engine stop. A length of time of this purging, however, is
limited up to the maximum duration time of purifier operation in
consideration of discharge from the battery.
The air pump is operated until the difference between the exhaust
pipe temperature TEX and ambient air temperature TAMB reaches a
specified value. If estimated exhaust pipe temperature and/or
estimated ambient air temperature is used, an appropriate length of
time of operation according to the exhaust pipe temperature after
the engine stop is specified and the pump is operated for the
specified length of time.
FIG. 7 is a flowchart of the control.
To begin with, whether the engine is at a stop is judged.
If the engine is at a stop, whether the secondary air pump
operation timer count is zero is judged. If the timer count is
zero, the secondary air pump is stopped.
If the timer count is other than zero, the timer count is
decremented by every specified length of time. At the same time,
the exhaust pipe temperature and ambient air temperature are
monitored and the temperature difference is calculated.
If the temperature difference is lower than a specified value, the
timer count of the secondary air pump is cleared.
If the engine is in operation after the engine has started, whether
the engine operating condition is under a specified condition is
judged. If the water temperature is higher than the specified and,
at the same time, the rotational speed of the engine is lower than
the idling speed by K2NDPND (several thousands r/min), the timer
for the catalyst temperature increase control is actuated and the
timer count is incremented by every specified length of time.
If the timer count for the catalyst temperature increase control is
less than the specified and, at the same time, the exhaust pipe
temperature is lower than the specified, the secondary air pump is
operated.
At the same time, the suction air volume and rotational speed of
the engine are obtained to calculate a basic fuel injection
volume.
If no exhaust pipe temperature sensor is available, the suction air
volume in every specified length of time is totalized and an
estimated exhaust gas temperature is calculated from the total. The
estimated exhaust gas temperature is filtered at every specified
unit time to obtain the exhaust pipe temperature. Instead of the
total suction air volume, total fuel injection volume can be used
for the above.
While the secondary air pump is in operation, a correction
coefficient for the individual air-fuel ratio control of cylinders
is calculated. For example, three different correction
coefficients, rich-side correction coefficient, stoichiometric
correction coefficient and lean-side correction efficient, are
obtained according to the timer of the timer for the catalyst
temperature increase control.
Three different values are selected one by one for every fuel
injection timing and corrected into the basic fuel injection
volume. It is also permissible to select the three values at every
specified unit time and corrected into a basic fuel volume.
Besides the individual air-fuel ratio control of cylinders, if a
means for increasing the catalyst temperature, by which the
ignition timing is retarded so as to combust the exhaust gas inside
the exhaust pipe, is employed additionally, the temperature
increases more quickly.
After the specified exhaust pipe temperature has been reached or
the timer setting of the catalyst temperature increase control has
elapsed, the secondary air pump is stopped.
If the catalyst temperature drops even in an idling state under
normal ope ration condition, as shown in FIG. 8, it is permissible
to clear or decrement the timer count of the catalyst temperature
increase control and restart the catalyst temperature increase
control.
The secondary air pump operation after the engine has stopped can
be continuous but, in consideration of the battery discharge after
the engine stop, it may be intermittent operation. Intermittent
operation can be, for example, such that a length of the operating
time is set per cycle of operation in accordance with the catalyst
temperature or that the operating time is set in accordance with
the decrease ratio at which the catalyst temperature decreases in
every specified length of time after the engine has stopped. Brief
description of the operation is show n in FIG. 9.
Although the air volume of the secondary air pump needed for
processing the exhaust gas during the engine operation is
relatively big, the air volume for cooling the exhaust pipe after
the engine stop can be minimal because air for proc essing the
exhaust gas is not needed. Because of the above, the size of the
secondary air pump necessary for the present invention can be
smaller than that of the secondary air pump used for processing the
exhaust gas during the engine operation.
For the same reason, it is permissible to install the secondary air
pump to be used during the engine operation separately from the
secondary air pump to be used after the engine stop and the one to
be used after the engine stop is made smaller in size or that the
rotational speed of the secondary air pump to be used after the
engine stop is set lower than that of the one to be used during the
engine operation.
A control method available for switching the rotational speed can
be such that the voltage applied to the secondary air pump is
switched or that the battery voltage is controlled by duty so as to
control the mean voltage.
If the basic battery voltage is 42 V, which means three 14-V
batteries are connected in series, it is also permissible to
install a connection switching circuit that applies the voltage of
one battery out of the three to the secondary air pump while the
engine is at a stop. An embodiment using this circuit is shown in
FIG. 10.
FIG. 11 shows the disconnection and short-circuit diagnosis of the
exhaust pipe temperature sensor, catalyst temperature sensor and
secondary air pump.
If the exhaust pipe temperature sensor voltage or catalyst
temperature sensor voltage is outside a specified range, the sensor
is judged to have failed and the fail-safe function, to be
described later, is actuated. When the exhaust pipe temperature or
catalyst temperature is to be estimated, the cooling eater
temperature or suction air temperature is used as a parameter. For
this reason, if the water temperature sensor or suction air
temperature sensor has failed, the fail-safe function is also
actuated.
An applicable concrete fail-safe function may be such that the
secondary air pump is operated according to a specified length of
time after the engine stop irrespective of the exhaust pipe
temperature of catalyst temperature.
If the CPU output for operating the secondary air pump does not
agree with the mode of the output terminal of a control unit, for
example, the CPU output is ON while the control unit is OFF or the
CPU output is OFF while the control unit is ON, the output of the
secondary air pump is judged to be faulty. If this happens, the VB
connected to the secondary air pump is cut open.
Besides, if the increase speed of the exhaust pipe temperature is
too quick or too slow, something abnormal has possibly been caused
in the exhaust pipe or secondary air system. If this happens, the
control system is judged to have failed.
If a failure is detected, failure information is stored in the
self-diagnosis storage area in the control unit and a failure
indication lamp MIL is lit to inform the operator of the failure of
the engine control system and also to ask for necessary repair of
the system.
In order to reduce the exhaust gas level, not only high catalytic
performance is needed but also discharge of the exhaust gas needs
to be controlled while the engine is at a stop. In a certain case,
for example, unburnt HC component of the exhaust gas remains in the
combustion chamber after the engine has stopped. Besides, if fuel
leaks out of the injector, it directly becomes unburnt HC even
though the volume is very small.
In order to discharge the unburnt HC component from the combustion
chamber, both exhaust valve and suction valve of the combustion
chamber are fully opened and also the throttle valve or ISC valve
is opened to let the gas out from the intake manifold side. FIG. 12
shows a timing chart.
If the exhaust valve and suction valve cannot be opened
independently, the crankshaft is rotated, using a device such as
starter, for a specified number of times or up to a specified crank
angle. And then, the rotation is stopped at a crank angle where the
suction valve and exhaust valve are set open.
If there exists no overlapped angle where the suction valve and
exhaust valve are set open at the same time, the rotation is
stopped at a crank angle where at least the suction valve side is
set open.
While the crankshaft is rotated for a specified number of times or
up to a specified crank angle, it is also possible to supply the
secondary air into the exhaust pipe so as to discharge the exhaust
gas from the exhaust pipe side to the intake manifold side.
In order to prevent fuel leakage from the injector, the fuel
pressure in the fuel pipe is reduced immediately after the engine
has stopped. Residual fuel in the fuel pipe is immediately returned
back to the fuel tank by means of, for example, installing a bypass
valve for bypassing a pressure regulator, bypassing the fuel pump,
or reversing the fuel pump operation.
Although the inlet of the secondary air is made on the upstream
side of the catalyst in the above embodiment, it is also possible
to install it near the exhaust valve of the engine so as to better
mix the exhaust gas and secondary air.
For example, the exhaust gas and secondary air are better mixed by
supplying the secondary air towards and over the exhaust valve as
shown in FIG. 13.
It is also permissible to install the secondary air inlet on both
the upstream side of the catalyst and the exhaust valve side.
It is also possible to construct a system where a branch valve is
installed in the secondary air piping so that the secondary air is
let only into the exhaust valve side during the engine operation
and into the upstream side of the catalyst after the engine has
stopped.
The above-mentioned embodiments are so constructed that the
secondary air control is performed only in the engine control unit.
However, if whether the engine is in operation or at a stop can be
judged, the secondary air pump can be controlled accordingly, and
therefore, the secondary air pump control as shown in FIG. 14
becomes available. That is, whether the engine is in operation is
judged based on an input signal relating to the engine rotation,
such as a crank angle signal; the engine is judged to be at a stop
if no crank angle signal is inputted for a specified length of
time, and the secondary air pump is controlled accordingly.
Beside, it is likely to happen that water enters from the muffler
side of a car in the outside if it rains or snows. If a car parked
in a garage for a long time is moved to the outside under intense
sunlight and the exhaust pipe temperature or catalyst temperature
is still low immediately after the movement, the exhaust pipe
temperature or catalyst temperature may become lower than the
due-point temperature and so it is also possible that water vapor
is sucked into the catalyst from the muffler side.
In consideration of the cases where water vapor adheres onto the
downstream side of the catalyst as explained above, it is also
possible to install the secondary air inlet on the downstream side
of the catalyst as shown in FIG. 15.
The above can prevent adhesion onto the catalyst of the water vapor
sucked from the muffler side.
Because the water content in the residual exhaust gas can be
prevented from liquefaction and adhesion onto the surface of the
catalyst, the catalytic performance of the exhaust gas purifier can
be maintained and, because no thermal stress is generated in the
catalyst support, reliability of the catalyst can be improved.
Besides, it becomes possible to use the catalyst for a longer
period o f time than in a prior art.
Although the present invention has been illustrated and described
with respect to exemplary embodiment thereof it should be
understood by those skilled in the art that the foregoing and
various other changes, omission and additions may be made therein
and thereto, without departing from the spirit and scope of the
present invention. Therefore, the present invention should not be
understood as limited to the specific embodiment set out above but
to include all possible embodiments which can be embodied within a
scope encompassed and equivalent thereof with respect to the
feature set out in the appended claims.
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